Quick match
Jump into a public server. Maps rotate every round.
Custom match
Private lobby with a code. Invite friends, pick the mode, map and bots, then start.
Practice
Private sessions. Nothing here changes your rank.
Dummies from 10 to 100 m (static, strafing, crouching), wallbang props, a CQB house and a grenade yard with a trajectory preview. Infinite ammo; you cannot be hurt.